The NSW government has refused to release the names of corporations enjoying the greater part of its $1.8 billion in tax breaks lest they be exposed to "harsh public criticism" and scrutiny, documents released under freedom of information reveal.

NSW Premier Gladys Berejiklian was making good on a deal that dated back to John Howard's GST.Credit:AAP

But the state government is refusing to release a list of the businesses that will benefit the most from the tax cuts, likely to include commercial property developers, to spare singling them out for public scrutiny.

But Labor argues information about where the government is directing money through tax breaks is fundamental to judging a government's priorities.

"Harsh public criticism ... is afforded to corporations when it is publicly revealed that they paid a level of tax that is not in line with community expectations," the Department of Finance wrote last year, upholding its initial decision to keep the information secret.

Although the department said there was no one reasonable public test for a reasonable corporate tax bill the community had shown interest in tax minimisation and referred to recent news reports showing up to one-third of private corporations paid no tax in 2013-14.

But releasing the information might undermine confidence in the state's confidential revenue ability or the secrecy provisions of NSW tax laws, which outweighed the public's right to know, it concluded.

"I am satisfied that if this type of criticism is levelled against any of the corporations mentioned in the document, then this would have the potential to prejudice their legitimate business, commercial or financial interests," the department said.

But Labor MLC Daniel Mookhey, who had for a year led a fight that has even involved the Crown Solicitor only to secure a de-identified list that showed that the state's largest company was paying up to $3 million each in business mortgage duties, argues the public has been denied information it needs to judge the government's budget priorities.

Mortgage duties are short-term loans secured against one property to finance or refinance the construction, acquisition of another, meaning large property developers and investors are potentially among the biggest beneficiaries of its abolition.

"They are the first government in memory who doesn't want people to know about their tax cuts," Mr Mookhey said. "How can parents decide whether these tax cuts are more important than clearing the record high-school maintenance backlog if the government won't tell them who are the biggest winners?"

NSW originally promised to axe the taxes in a 1999 agreement with the Howard government after agreeing they would receive a greater proportion of GST revenue.

But a series of a state governments, including the O'Farrell government, deferred a promise to axe the taxes following NSW's share of falling GST revenue.

A spokesman for the acting Treasurer, Victor Dominello said: "[Freedom-of-information] decisions are made independently by the Department and remain at arm's length from the Minister to protect the integrity of the process.

"Decisions regarding the release of sensitive information, such as individual and company tax liability, must balance privacy rights with the broader public interest."